1. Field of the Invention
The invention relates to a method of spoke filling for radar scan converter and a spoke filling processing unit for the same.
2. Description of the Related Art
FIG. 1 shows a block diagram of a conventional radar scan converter. The radar scan converter 100 shown in FIG. 1 is a new generation of plan position indicator prominent in the technology trend. The used method converts the polar coordinates of the radar video into Cartesian coordinates through the coordinate converter 102. The cartesian coordinates then are output in a raster scan fashion to the monitor 104. Because of the innate characteristics of the coordinate conversion, the correspondence between the echoes and the conversion into cartesian coordinate points is different depending on whether the echoes are at short distance, medium distance, or long distance from the reference point of the radar sweep line. In the case where the polar video points are in short distance, there is no one-to-one correspondence between the polar video points and the corresponding Cartesian points, and more than one polar points can correspond to a single Cartesian point. This occurrence of point repeated hitting is conventionally called xe2x80x9ccollisionxe2x80x9d. The collision can cause the lifetime of the display point to be shortened. In the case where the echoes are at medium distance, the one-to-one correspondence can be obtained. And, at long distance, there are many cartesian points that cannot be corresponded to any polar point, which causes the occurrence of spokes.
In FIG. 1, the AZ_sync signal, delivered to the coordinate converter 102 and the FIFO buffer 106, is the radar azimuth signal that comprises the azimuth reference pulse (ARP) and the azimuth change pulse (ACP). When the antenna rotates, each scan has 4096 azimuth change pulses (ACP) and 1 azimuth reference pulse (ARP), the azimuth reference pulse (ARP) appears when the antenna faces to the north during the rotation. The Trigger signal delivered to the coordinate converter 102, the timing generator 108 and the A/D converter 110 represents the moment when the radar wave is triggered and from which the counting of the distance starts. According to the signals AZ_sync and Trigger, the coordinate converter 102 evaluates the polar coordinates (r, xcex8) of the radar video that then are converted into Cartesian coordinates (x, y). According to the Cartesian coordinates (x, y) of the points, the occurrence of spokes between the two neighboring sweep lines are determined, the spoke filling then is performed via the spoke filling processing unit 112. The overlay processor 114 integrates the radar video, the graphic and the text which are generated from the computer display unit (not shown).
FIG. 2 illustrates the method of spoke filling calculation procedure, according to the U.S. Pat. No. 4,697,185 issued to Thomas et al. If 0xc2x0xe2x89xa6xcex8xe2x89xa645xc2x0, a point (xi, yi) is selected on the sweep line L.
(1) A point (xixe2x80x2, yixe2x80x2) is selected on the sweep line Lxe2x80x2 next to the sweep line L, wherein yi=yixe2x80x2, and xixe2x80x2=r cos xcex8 tan xcex8xe2x80x2 from the geometrical relationship.
(2) If xixe2x80x2xe2x88x92xi greater than 1, there is at least a spoke occurrence; the series xi+1=xi+1 is then constructed till xixe2x80x2xe2x88x92x1+nxe2x89xa61, such that the n points (xi+1, yi), (x1+2, yi), . . . , (xi+n, yi) are filled up (this filling fashion is called horizontal fashion spoke filling).
(3) As shown in FIG. 2, the video value of the point (xi+1, yi) is taken from the video value of the point P which distance from the reference center O on the sweep line L is r+sin xcex8. In the same manner, the video value of the point (xi+2, yi) is taken from the video value of the point Q which distance from the reference center O on the sweep line L is r+2 sin xcex8, etc. till r+n sin xcex8.
(4) If 45xc2x0xe2x89xa6xcex8xe2x89xa6135xc2x0 or 225xc2x0xe2x89xa6xcex8xe2x89xa6315xc2x0, the vertical fashion spoke filling is applied as follows. For example, when 45xc2x0xe2x89xa6xcex8xe2x89xa690xc2x0, the foregoing steps are changed into yixe2x80x2=r cos xcex8 cot xcex8xe2x80x2. If yixe2x88x92yixe2x80x2 greater than 1, there is at least a spoke occurrence, and the series yi+1=yixe2x88x921 is constructed till yi+mxe2x88x92yixe2x80x2xe2x89xa61, such that the m points (xi, yi+1), (xi, yi+2), . . . , (xi, yi+m) are filled up.
The U.S. Pat. No. 5,530,450 issued to Sohn et al. relates to a spoke filling method wherein the sweep line plane is divided into four regions (region 0xcx9c3), as shown in FIG. 3. Two adjacent regions are such that the number of sweep lines of the outward region is the double increase of that of the inward region. This specific arrangement allows the spokes at long distance from the reference center to be filled.
The U.S. Pat. No. 5,554,992 issued to Toth et al. discloses a spoke filling method similar to the method of Sohn. The difference specifically lies in the applying of hyperbolic curves to divide the sweep line region, wherein the multiple increase of the sweep lines begins at the point which is the first spoke from the reference center (called xe2x80x9cbreak pointxe2x80x9d).
Some phenomena should be considered from the foregoing conventional methods. Thomas et al.""s method may be deficient when the sweep line meets two adjacent points (xi, yi) and (xi+1, yi) with the same coordinate yi as shown in FIG. 4, which causes a collision. As a result, the spoke filling cannot be effectively completed. Moreover, a lot of memories are needed to store (cos xcex8 tan xcex8xe2x80x2) numerical values and (cos xcex8 cot xcex8xe2x80x2) numerical values.
With respect to the methods of Sohn et al. and Toth et al., the collision is unfavorably frequent. Besides, the design of the electrical circuit to implement the methods is relatively complicated and the usage of memory is increased.
A major aspect of the present invention is to provide a method of spoke filling for radar scan converter and also a processing unit that implements the same method in which the spoke filling can be efficiently performed while the collision issue is overcome.
To attain the foregoing and other objectives, the present invention provides a method of spoke filling for radar scan converter that, according to a preferred embodiment, comprises first, comparing the coordinate sector of a second sweep line with the coordinate sector of a first sweep line, wherein both adjacent sweep lines are referred to as respectively a present sweep line and a previous sweep line. The comparison of the coordinate sector values determines whether either a horizontal fashion or a vertical fashion spoke filling should be applied. If the coordinate sector of the second sweep line is different from the coordinate sector of the first sweep line, the sector value and the points of the second sweep line with their respective video value are stored in a memory. If the coordinate sector of the second sweep line is identical to that of the first sweep line, the sector value and each of the points of the second sweep line with their video value are stored in a buffer. The spoke filling thus is performed between the first sweep line points stored in the memory and the second sweep line points stored in the buffer. The determination of whether either a horizontal or vertical spoke filling should be applied is in accordance with the coordinate sector value stored in the buffer (that is the sector value of the second sweep line). Then, each of the cartesian points of the second sweep line is compared to each of the corresponding cartesian points of the first sweep line to obtain either an abscissa or ordinate difference, wherein the corresponding cartesian point of the first sweep line is, according to either a horizontal or vertical spoke filling, either the point that has the same ordinate or the point that has the same abscissa. If the difference is greater than +1 or less than xe2x88x921, all the points that are located between the cartesian point of the second sweep line and the cartesian point of the first sweep line are filled with the video value of the point of the second sweep line; if the difference is equal to +1 or xe2x88x921, the cartesian coordinates of the point of the second sweep line with its video value and the coordinate sector of the second sweep line are stored in the memory to update respectively the cartesian coordinates of the point of the first sweep line with its video value and the coordinate sector of the first sweep line; and if the difference is equal to zero, the maximum value between the video value of the point of the first sweep line and the video value of the point of the second sweep line is chosen to update the video value of the first sweep line.
To attain the foregoing and other objectives, the present invention provides, according to another embodiment, a radar scan converter that comprises a buffer, an overlay processor and a spoke filling processing unit. The buffer, when receiving a read signal from the spoke filling processing unit, provides the spoke filling processing unit with the coordinate sector, the cartesian coordinates, and the video value of the second sweep line. When a spoke point, between the first sweep line point and second sweep line point, has been processed, the spoke filling processing unit outputs the coordinates of the corresponding pixel to be filled with its corresponding intensity value to the overlay processor.
To accomplish the spoke filling according to the spoke filling method of the present invention, the spoke filling processing unit comprises a timing generator, a first and a second multiplexers, a memory and a finite state machine. The memory is directed to store contents related to the first sweep line, comprising the coordinate sector and the points of the first sweep line with their respective video value. The multiplexers are directed to process and provide the finite state machine with the contents related to the coordinates of the single point of the second sweep line that is currently processed. From the contents related to the points of the first sweep line and the contents of the points of the second sweep line and with the coordination of the timing generator, the finite state machine conducts the spoke filling between the first and second sweep lines by simultaneously taking into consideration collision occurrence.
By achieving the above spoke filling method with the above spoke filling processing unit, the spoke filling can be efficiently performed with a substantially small quantity of memory, while the collision can be avoided.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.